This invention relates to improved methods and images for displaying Doppler tissue information in an ultrasonic imaging system.
Arenson et al. U.S. Pat. No. 5,285,788 discloses a Doppler tissue imaging method that forms an ultrasonic image of moving tissue. Stationary tissue is suppressed in the image since the Doppler signal is sensitive only to moving targets. In Doppler tissue imaging (DTI) standard clutter filters that block ultrasonic signals associated with low speed targets are made less restrictive, and the DTI image includes image information for slowly moving tissues such as the heart wall. Doppler tissue imaging can be performed using tissue velocity, energy or acceleration to form a two-dimensional image that is spatially coordinated with and superimposed on a conventional B-mode image. The B-mode image displays a tomographic image of both moving and stationary tissue, and the combination of DTI and B-mode images allows the selected Doppler tissue information to be displayed simultaneously with and superimposed on the tomographic B-mode image.
Doppler tissue imaging has an important role in a number of cardiology imaging areas such as endocardial border detection, myocardial wall motion investigations, regional wall motion investigations, and myocardial perfusion investigations. In many applications, high quality Doppler tissue imaging depends greatly on the temporal and spatial resolution of the combined image.
In conventional DTI, two separate frames of image information are acquired: a color Doppler frame and a spatially coordinated B-mode frame. These two frames of image information are then combined to produce the DTI/B-mode composite image described above. For each pair of frames (DTI and B-mode), time is spent in alternately firing B-mode acoustic lines and color Doppler mode acoustic lines. If the time required for acquiring one B-mode frame is T.sub.B and the time required for acquiring one Doppler frame is T.sub.D, the total DTI/B-mode composite frame requires (T.sub.B +T.sub.D) for acquisition, and the corresponding frame rate is 1/(T.sub.B +T.sub.D). The temporal resolution of the composite frame is fundamentally limited in this way.
A need presently exists for methods for increasing the time and/or spatial resolution of DTI images.